1. Field of the Invention
The present invention relates to an apparatus for estimating the direction of a sound source, and more particularly to an apparatus for estimating the direction or orientation of a sound source with respect to a reference position, such as head, of the body of a listener.
2. Description of the Background Art
Humans may recognize the location, such as direction and distance, of a sound source based on a difference in sound heard from the source between the right and left ears. Such a difference between the right and left ears is caused by a difference in distance to the sound source from the right and left ears, and hence differences in characteristics such as frequency, phase and intensity of the sound afforded during the sound being propagated in the air.
When intentionally controlling a sound signal received from a sound source as to a difference in such characteristics as stated above, the sound source may be recognized as located in the intended direction and at the intended distance with respect to the listener. It is so far known that a characteristic afforded to the sound propagated from a sound source to the ears may be well defined by an HRTF (head-related transfer function). When an HRTF is measured in advance from a sound source to the ears and then afforded to a sound source signal, the listener may recognize the sound as coming from an actual sound source. When the movement of the head of the listener is sensed to control the sound signal accordingly, he or she may recognize the sound source as being fixed in absolute location during the movement. For example, when the listener has his or her head turned rightwards or leftwards, the sound source signal may be controlled so as to shift the location of the sound source with respect to the head towards left or right, respectively, thus rendering the listener feel that the sound source is stationary in fact.
As a measure of detecting the orientation or movement of the head of a listener with respect to a sound source, there is known a solution of employing the GPS (Global Positioning System) as disclosed by Japanese Patent Laid-Open Publication No. 2002-267737. There are also known so far a solution of employing an acceleration sensor, as disclosed by Japanese Patent Laid-Open Publication No. 2003-139536, and another solution of utilizing a geomagnetic sensor, as disclosed by Japanese Patent Laid-Open Publication No. 2003-167039.
The conventional solutions disclosed by the above-indicated patent publications are in need of dedicated hardware and thus suffer a problem on the increasing size and cost of the devices.